Abstract Flood is a naturally occurring disastrous event causing damages, losses and destruction to property, life and environment. Hundred millions of money are spent every year in flood control and flood forecasting. For construction of any structure near by a water body or in between a water body and for determination of safe levels of construction to protect structure from flood water, safe grade elevation is required. In order to evaluate or estimate, mitigate and handle the floods, the present paper presents a methodology for assessment of flood line to produce safe grade elevation by using River Analysis System made by Hydrologic Engineering Center (HEC-RAS) software which is predominately used in the field of hydraulic analysis for floodplain delineation. The general parameter affecting flood is runoff gauge, discharge, rainfall and land use as spatial data. This paper explains the use of the HEC-RAS for producing the safe grade elevation for Mutha River from its origin at downstream side of Kadakwasla dam till Mahtre Bridge. It explains the methodology to construct a table model and how to validate it. The methodology developed can be applied for regions if only predominant factors affecting the flood in that region is consider, to decide the best economical safe grade elevation for the building or structure near or on the river and would help in planning priorities prerequisites for managing flood efficiently. Keywords: Safe Grade elevation, Parameters, Mutha River, Flood, spatial data, Zoning.

1. IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
_______________________________________________________________________________________
Volume: 05 Issue: 01 | Jan-2016, Available @ http://www.ijret.org 125
DETERMINATION OF SAFE GRADE ELEVATION BY USING HEC-
RAS: CASE STUDY MUTHA RIVER
Ritica Thakur1
, Deepali. R. Vaidya2
1
M.E Second Year Hydraulics student, Department of Civil Engineering, Sinhgad College of Engineering, Pune
University, SCOE Vadgaon (BK), Pune, Maharashtra, India.
ritica.thakur@gmail.com
2
Asst. Professor, Department of Civil Engineering, Sinhgad College of Engineering, Pune University, SCOE Vadgaon
(BK), Pune, Maharashtra, India.
drvaidya.scoe@sinhgad.edu
Abstract
Flood is a naturally occurring disastrous event causing damages, losses and destruction to property, life and environment.
Hundred millions of money are spent every year in flood control and flood forecasting. For construction of any structure near
by a water body or in between a water body and for determination of safe levels of construction to protect structure from
flood water, safe grade elevation is required.
In order to evaluate or estimate, mitigate and handle the floods, the present paper presents a methodology for assessment of flood
line to produce safe grade elevation by using River Analysis System made by Hydrologic Engineering Center (HEC-RAS)
software which is predominately used in the field of hydraulic analysis for floodplain delineation. The general parameter affecting
flood is runoff gauge, discharge, rainfall and land use as spatial data. This paper explains the use of the HEC-RAS for producing
the safe grade elevation for Mutha River from its origin at downstream side of Kadakwasla dam till Mahtre Bridge. It explains the
methodology to construct a table model and how to validate it. The methodology developed can be applied for regions if only
predominant factors affecting the flood in that region is consider, to decide the best economical safe grade elevation for the
building or structure near or on the river and would help in planning priorities prerequisites for managing flood efficiently.
Keywords: Safe Grade elevation, Parameters, Mutha River, Flood, spatial data, Zoning.
--------------------------------------------------------------------***----------------------------------------------------------------------
I. INTRODUCTION
A flood is a condition of unusually rise in stage of a river, it
is the level at which the banks of river overflows and the
adjoining area inundates. India is enlisted as most flood-
affected countries of the world.
Floods cause severe bank erosion if the river banks are
fragile and not protected against the heavy flood discharges.
Loss of life, economic loss and loss of property are all
results caused by floods. There are two options for flood
management viz. structural measures & non-structural
measures. The modern flood management strategy is a
judicious mixture of both options. For this hundreds of
millions of money are spent every year in flood control and
flood forecasting. Flood proofing of important structures is
also accomplished by combination of adjustment and / or
addition of features to buildings that eliminate or reduce the
potential for flood damage. One of them is by providing
safe elevation to the building. For the construction of any
structure near by a water body or in between a water
body, determination of safe levels of construction is find
out to protect the structure from flood water. This elevation
is called as safe grade elevation. Safe grade elevation is the
elevation given to the building as a height or plinth height to
stop the intrusion of water into the building.
This measure is used for the construction of important
power projects, buildings and other structures. The guideline
of National Disaster Management Authority, Government of
India also recommends that the installations of national
importance structure i.e. important structures with respect to
life of people or money should always be above the
specified flood level for example Nuclear power plant,
Bridges, industries or any residential projects, etc. For the
safety of the structure it is recommends that in addition to
the flood caused by precipitation, other possible flood
sources are to be evaluated for estimation of maximum flood
level.
Safe grade elevation is calculated by knowing the maximum
stage of the river in previous years and the worst probable
stage the river may have. This can be achieved by
computing the surface profile computation of the river for
different discharged condition of the river. We are using
HEC-RAS software for generation of the one dimensional
surface profile model of the surface of the Mutha River.
US Army Corps of Engineers (1982) Hydrologic
Engineering Centre developed HEC-RAS, which is based on
standard step method. It is being widely used in many
countries for water surface profile computations and proved
to be very accurate and useful.

2. IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
_______________________________________________________________________________________
Volume: 05 Issue: 01 | Jan-2016, Available @ http://www.ijret.org 126
HEC-RAS is a program which performs water surface
profiling in one dimension. To generate model in HEC-RAS
requires definition and descriptions of the land surface and
hydrologic events flow data. The flow data and geometric
data are used to calculate gradually, steady, varied flow
water surface profiles (steady-flow module) from energy
loss computations. HEC-RAS is capable of performing a
modelling a full network of a dendrites system, channels, or
a single reach.
II. LITERATURE REVIEW
In a paper presented by Guan Tie-sheng. This paper
discusses the flood safety of the Banqiao and estimation of
inflow flood designed parameters. After performing flood
routing, they concluded that 117.76 m of water level and
2000 m3
/s of maximum discharge as 100-year floods
parameter; 118.92 m of water level and 13500 m3
/s
maximum discharge as 5000- year flood parameter, and
119.63 m of water level and 14400 m3
/s of maximum
discharge as 10000-year flood parameter .
A report drafted by CWPRS which discuss one and two
dimensional model studies for prediction of changes in flow
conditions in Panvel creek due to development of proposed
International Airport at Navi Mumbai, Maharashtra.
CWPRS, Pune, conducted a one dimensional model study
by using Charima. A two dimensional plot was prepared by
using MIKE 21, showing the difference in maximum
velocity between with and without airport cases. The tidal
water levels predicted from the Charima model and the
MIKE 21 model are in close agreement.
A report was drafted for estimating the designed flood and
safe grade elevation for nuclear power project at Gorakhpur,
Haryana. In this Report, the hydrological analysis had been
performed on basin boundary and was extended to districts
of Jind, Kaithal and Hissar to study the safe grade elevation
for the nuclear power plant. MIKE 11 software was used for
one dimensional modelling of dam break analysis of Bhakra
Dam. Mike 21 HD Model two-dimensional flow modelling
was done. The MIKE FLOOD model had been set up for
both the case and the model results had been studied. Flood
estimation was performed by six different methods. The
contour planning results into development of land to safe
grade elevation of all the grid points, while the general
topography of the plant site is retained. This is helping in
design for runoff generated from local site rainfall.
Mr. Sina Alaghmand presented a paper on comparison of
two hydraulic models in regards to their capabilities of river
flood risk analysis. A softer developed by Danish Hydraulic
Institute (DHI) as MKE11 and by US Army Corps of
Engineers as HEC-RAS4.0 is capable of performing river
flood risk analysis. Comparison was made on the four
aspects those are available outcomes, credibility, the
availability and usability of the models. In this research
Sungai Kayu Ara River basin was studied as case study
which is located in Kuala Lumpur, Malaysia. Later observed
water levels were compared against the results of the
models. This research concludes that for river flood risk
mapping HEC-RAS has more capabilities in comparison
with MIKE11.
Mr. Smemoe in his paper on “Developing a Probabilistic
Flood Plain Boundary Using HEC-RAS-1 and HEC-RAS”
has discussed about probabilistic flood plain boundary
development by using HEC-RAS and HEC-RAS-1.
In this paper an approach is developed for flood plain
boundary to incorporate uncertainty in the modeling
parameters during model development. Some general
conclusions were made by the author for any project, on the
bases of basic engineering principles similar solutions can
be obtained while developing Flood Insurance Rate Map
(FIRM). A develop a better modeling approach to get a
flood plain boundary will requires integrated approach of
uncertainty as the modeling parameters during model
development. Delineation tools as a Computer operated
flood plain is used to determine inundation depths and flood
plain boundaries as the solutions of the series model. Finally
a solution is generated in the form of probabilistic flood
plain map. The contour on probabilistic flood plain shows
percent probability of flooded location.
III. CASE STUDY
In the present study a Hypothetical case study of a
construction site situated at the bank of river Mutha at seven
Km downstream side of Khadakwasla Dam Project is
consider.
For the study of such a site we had consider a reach of 10
Km of river Mutha from the downstream side of the
Khadakwasla Dam. The Mahatre Bridge is selected as the
gauging bridge site for the validation of the model. Tabel1
describes the data required. The data is collected from the
irrigation offices, data user group and topographic sheets.
The observed data for the application of the unit
hydrographs approach were not available. Hence, in this
study the synthetic unit hydrograph was derived using the
estimation of flood.
Report for the Krishna and Pennar Subzone-3(h) is used as
the base of the design of the discharge calculation for the
R25, R50, R100.
Table1:- Description of data required and purpose
Sr.
No.
Data Required Purpose
1. Cross section details of
the river.
Construction of
Table Model
2. Catchment area of the
Kahadakwasla Project
Rain fall Analysis
And
Return flood
3. Flood reports.
4. River Gauging Data Discharge data of the
Khadakwasla dam
5. Discharge data of the
Khadakwasla dam

3. IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
_______________________________________________________________________________________
Volume: 05 Issue: 01 | Jan-2016, Available @ http://www.ijret.org 127
IV. METHODOLOGIES
A. Analytical: - Design flood estimation is done by using
various flood formulas. To design the flood the best
analytical method is SUG method if scanty data is available.
A. Estimation of Extreme Rainfalls of Various Return
Period: - To design flood estimation Probable Maximum
Flood (PMF) using the synthetic unit hydrograph approach,
the floods of various return periods using the Gumbel’s
based frequency analysis is found out. Gumbel (1941)
introduced extreme value distribution and that is called as
Gumbel distribution. It is most popular and adopted
probability function for doing extreme values modelling of a
random variable in hydrologic and metrological studies for
the prediction of maximum wind speed, maximum rainfalls,
etc. SUG method is based on the Unit Hydrograph method.
B. Design Strom: - To predict peak flood hydrograph unit
hydrograph technique is used. Extreme rainfall situation
were used to generate the design storm parameters. Detailed
information about the rainfall and the resulting flood
hydrograph were used to develop unit hydrograph for the
selected catchment. But this information would be available
for only few locations and will be very scanty. Majorities of
the catchment areas, especially those which are located at
remote locations always suffer with such conditions.
Empirical equation of regional validity which relate the
salient hydrograph characteristics to the basin characteristics
are available and used to construct unit hydrograph for
selected catchment area. The unit hydrograph derived using
these relationships are called as synthetic unit hydrographs.
SUG is a unit hydrograph of unit duration for a catchment
developed. These unit hydrographs are based on the relation
established between physiographic and unit hydrograph
parameters of the representative gauged catchments in
hydrometeorologically homogeneous region. It is possible to
develop unit hydrograph if the site specific concurrent
rainfall run-off data for every site is available for 5-8 years.
Derivation of SUH (Synthetic Unit Hydrograph)
Procedure to obtain parameters based on physiographic
characteristics of the catchments and establishing
relationship between physiographic parameters and unit
hydrograph parameter to develop SUG is described in
following paragraphs.
Physiographic Parameters
The physiographic parameters considered in the present
study are:-
Catchment Area (A): - The gauging site is located on
toposheet and the watershed boundary is marked. The area
enclosed in this boundary up to the gauging site may be
referred to as “A” as catchment area.
Length of Main Stream (L):- This implies the length of the
longest main river/nala/stream from the farthest point on the
watershed boundary of the selected catchment area to the
gauging site.
Length of the main stream from the observation site to
point near the centre of gravity of catchment (Lc):- For
finding the centre of gravity of the catchment. Usually the
boundary of the catchment is cut on a cardboard, which is
then hung in three different direction in vertical planes and
the plumb line are drawn from the point of hanging. The
point of intersection gives the centre of gravity of selected
catchment but the nearest point to the centre of gravity is
consider to find the length of the main river from the centre
of gravity to the point of study (Lc).
Equivalent Stream slope (S):- One of the physiographic
parameter is slope. The slope may be equivalent or
statistical. In the present study equivalent stream or the
slope has been replaced with statistical slope. Equivalent
slope can be computed by analytical method .In this method
L- section is broadly divided into 3 or 4 segments
representing the broad ranges of the slopes of the segments
and the following formula is used to calculate the equivalent
slope (S):-
S = [∑ Li (Di-1 + Di)] / (L)2
Where,
Li = Length of the ith
segment in km
Di-1, Di = Elevation of river bed at ith
, intersection
point of counter reckoned from the bed
elevation at points of interest considered
as datum and Di-1 and Di were the highest
of the successive bed location at counter
and intersections.
L = Length of the longest steam in km
A simplified approach for calculating the Q25, Q50, Q100 one
of the method is Regression analysis. In these equations
dependent variables are related to their respective
physiographic parameters, A, L, LC and 24 hour point
rainfall values. Following equation are used for calculation
of 25 year, 50 year and 100 year flood discharge for each
gauged catchment. [12]
Q25 = 0.4285 (A)0.733
(L)-0.264
(LC)0.264
(R25)1.426
Q50 = 1.69432 (A)0.753
(L)-0.338
(LC)0.304
(R50)0.934
Q100 = 8.33488 (A)0.793
(L)-0.422
(LC)0.313
(R100)0.416
Where Q25, Q50, Q100 are 25 year, 50 year and 100 year flood
in cumec respectively.
A is the catchment area up to point of study in Sq.km.
L is the length of the longest main stream along the river
course in km
LC is the length of the longest main river/steam /nala from a
point opposite to the centroid of the catchment area to the
gauging site along the main stream in km.
R25, R50, R100 are 24 hour point rainfall values in cm for the
return flood of 25 year, 50 year and 100 year return period
respectively.

4. IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
_______________________________________________________________________________________
Volume: 05 Issue: 01 | Jan-2016, Available @ http://www.ijret.org 128
Compression between the result obtain is also studied for the
suitability of the result obtain for small catchment area
which is shown in the table 2.
B. Soft Computational: - Soft computational modelling is
done by using HEC-RAS. The program computes is based
on Standard step method. By solving the one-dimensional
energy equation water surface profiles from one cross
section is produced and similarly the next profile is also
produced [3].
This programme use momentum, continuity, and energy
equations which describe the relationships among various
flow variables, such as the discharge, flow depth, and flow
velocity. By solving these equations, it is possible to
determine the flow conditions throughout a specified
channel length. These analyses yield the change in flow
depth in a given distance or compute the distance in which a
specified change in flow depth will occur. The channel cross
section, bottom slope, the rate of discharge and Manning's n
are usually known for these computations of steady state
flow [3].
By differentiating the energy equation for a channel section
between two river sections, the governing equation for
gradually varied flow can be expressed as,
= (So- Sf)/[1- (aBQ2
)(gA3
)]
Where, S f is the slope of the energy-grade line, So is the
slope of the channel bottom, as the velocity head coefficient,
B is the bottom width of the channel, Q is the discharge and
A is the cross sectional area of the channel.
After calculating the value for Q25, Q50, Q100 a table model is
prepared with the help of HEC-RAS for Hydrological
analysis of the flood discharge. This modelling is done to
study the surface profile of the river at the time of the flood.
V. RESULT
By using this data the model is run for different returns
period floods and the surface profile of these discharge at
the selected site are taken as the level of water at the time of
flood. Table 2 shows the various discharge obtained by
using SUH Method and Regression analysis. The variation
of the result obtained with regression with respect to SUG is
not acceptable. Hence the discharge values obtain by SUH
method is used as an input to for the table model.
Table 2. Compression between SUG and regression result values
Sr. No Name of catchment area Return Periods By SUG By Regression Variation With Respect To SUG %
1 Khadakwasla R25 811.42 874.21 -7.738285968
2 Khadakwasla R50 923.7 1063.05 -15.0860669
3 Khadakwasla R100 988.24 1357.727 -37.38838744
4 Temghar R25 710.8133 792.6 -11.5060734
5 Temghar R50 780.0317 577.3242 25.98708488
6 Temghar R100 840.1414 422.4739 49.71395291
7 Varasgaon R25 1025.7 1161.9 -13.27873647
8 Varasgaon R50 1104.18 1020.144 7.610715644
9 Varasgaon R100 1182.08 927.8449 21.50743604
10 Pansheet R25 893.4732 1043.984 -16.84558641
11 Pansheet R50 962.8323 922.0161 4.239180593
12 Pansheet R100 1031.614 982.4364 4.767054344

5. IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
_______________________________________________________________________________________
Volume: 05 Issue: 01 | Jan-2016, Available @ http://www.ijret.org 129
The model is validated from the data provided for the
Mahtre Bridge gauging site. So elevation above that surface
is the safe grade elevation for the construction of the
building.
According to the functional and the economical importance
the safe grade elevation of the structures are selected.
VI. CONCLUSION
1. After validation of the model for the maximum
discharge on 30th
July 2006 and 11th
August 2006 for
Mahtere Bridge Site model was run for the return
period flood.
2. The level for the purposed site for R25 was found to be
553.71 m, for R50 was found to be 554.03m, for R100
was found as 554.29 m.
3. After studying this project following points can be
concluded
a. The HEC-RAS has better performance than the
MIKE11.
b. There is very less increase of flood discharge and level
of R25, R50 and R100.
c. SUH method for the flood design holds more accuracy
than regression equation for small catchment areas.
ACKNOWLEDGMENT
I am thankful to Hydrological Data user group, Centeral
Water Commission, Irrigation Department, Government of
Maharashtra for providing me Case study data. I would like
to thank Deputy Eng. Mrs. Deepgauri A. Joshi, Sectional
Eng. Mr. Khate for their kind Support and all who have
directly or indirectly helped me during the course of this
work, and whose names have been missed here to record.
REFERENCES
[1] Central Water Commission. CWC (1984) Flood
estimation report for Upper Indo-Ganga plains
(subzone-1e)
[2] “Estimation of Design Basis Flood and Safe Grade
Elevation for Nuclear Power Project at Gorakhpur,
Haryana” A report by CWPRS
[3] USACE, Hydrologic Engineering Centre, River
Analysis System HEC-RAS, Hydraulic Reference
Manual version 3.0, January 2001.
www.usace.army.mil
[4] National institute of hydrology (1999) “Computation
of water surface profile using HEC-RAS” CS (AR)-
30/98-99
[5] Http://www.mapsofindia.com/top-ten/geography/india-
flood.html
[6] Http://pune.nic.in/punecollectorate/punecity/climate.as
px
[7] Kumar, R. and Chatterjee, C. Regional flood frequency
analysis using L-moments for North Brahmaputra
Region of India. J. Hydrologic Engineering, ASCE,
10(1), 1-7 (2005).
[8] Kumar, R., Chatterjee, C. and Kumar, S. 2003
Regional flood formulas using L-moments for small
watersheds of Sone Subzone of India”. Journal of
Applied Engineering in Agriculture, American Society
of Agricultural Engineers. Vol. 19, No. 1, pp.47-53.
[9] Kumar, R., Singh, R.D., and Seth, S.M. (1999).
“Regional flood formulas for seven subzones of zone 3
of India.” J. of Hydrologic Engrg. ASCE, 4(3), 240-
244.
[10] Technical requirements for flood control and beneficial
purpose regulation management of Banqiao reservoir
reconstruction project [R]. Tianjing: Tianjing survey
and design institute, 1993.
[11] National institute of hydrology (1999) “Computation of
water surface profile using HEC-RAS” CS (AR)-30/98-
99
[12] Central water commission flood estimation report for
the Krishna and Pennar Subzone-3h
[13] Developing a Probabilistic Flood Plain Boundary
Using HEC-RAS-1 And HEC-RAS Smemoe, C.Nelson
J and Zundel A. (2003) World Water & Environmental
Resources Congress 2003
[14] One and Two Dimensional Model Studies for
Prediction of Changes in Flow Conditions in Panvel
Creek due to Development of Proposed International
Airport at Navi Mumbai, Maharashtra
Review of CWPRS Draft Report
[15] Identification and classification of flood prone areas
using AHP, GIS and GPS, Bhagat Madhuri, Ghare
Aniruddha and Ralegaonkar Rahul, .